WHY EYES ARE BLUE.

Dunstan Times, Issue 3333, 9 August 1926, Page 2

WHY EYES ARE BLUE.

j Th(.' color of the eye is determined j 1 1 y tlu> iris, tii-o circular curtain which I siiiTuund.s the aperture called the -pupil When examined under the microscope the iris is seen to be made up of a loose mesh work of irregularly shaped branch** ing “cells.” Each of these shells contains, scattered through it, minute granules or a brownish or blackish simstaneo called melanin (from the Cheek word for black)- ■ further, lining the back of the insthat is next the inside of the eye itsell .—is a double layer of cells of regular shape like bricks, which contain even more of the dark grannies than the irregular cells in front of them. Tins -deep pigmentation is for the purpose of preventing lignb passing into the eye except through the pupil any other than central light being purposely absorbed by the dark pigment in the iris. Jij common with almost all oLlie parts of the body, the iris contains blood vessels, bet us suppose linn there is no pigment in any of these layers of the' iris, a condition actnad> found in certain perfectly white aid mats and occasionally in human beings, who, though young, have white hair. These white animals are known as a' liinoH. The result here is that light, will penetrate the iris, and passing through a part that contains blood, u makes’ that part pink. The iris of an albino animal or hu man being is pink, lor exactly thy same reason that a. complexion is pin --tlic light is returning from a white but blood-containing tissue. Let us take the next case; an in which has the layer at the back /file with its usual pigment, but whose mes! work contains .few or none of the mela nil! granules. Here the light ear penetrate the meshwork. .but a .ere;’ deal of it s quenched bv the bluer, layer at the hack of the iris, Ihe re sill I • of this is'that smli light as returns- uimbsorhed to the observer seem to have a blue tint. The exact amount and distributin' of the melanin in the meshwork of the iris determines the exact k.nd of “light colored” eye, for we can distinguish -’ark Idue.’light blue, grey blue, green blue. and even other kinds of blur eyes. if the nieMiwock of tile iris is espe'■iallv full of melanin, the baht Hint -trikes it never reaches the black laver d’ccausc it is largely absorbed in I lie uav 1 - mesbw'-rk. If it is all absorbed, the eye is Ida eh : if less is quenched, it is brown. '1 lien-o-f; all gradations from bbicf; to a huht brown. Black am! brown ewes. Mi ere Fore, are due to the presence oi real dark pigment: whereas blue eve arc not due to any blue nignmni a I all. As i fe ad.vaiices. more and more -dement lends to he deposited in the iris, so that it (.-oiiies about llial infants born v.itb idm- eyes (as the vast majority are) acquire a different eye color before they have grown up.